EP1916446B1

EP1916446B1 - Gearbox with synchronising clutch

Info

Publication number: EP1916446B1
Application number: EP06255503A
Authority: EP
Inventors: Jeff Birkel; Alan Griffiths
Original assignee: Turner Powertrain Systems Ltd
Current assignee: Turner Powertrain Systems Ltd
Priority date: 2006-10-26
Filing date: 2006-10-26
Publication date: 2010-11-17
Anticipated expiration: 2026-10-26
Also published as: EP1916446A1; US7942074B2; ATE488711T1; DE602006018322D1; US20080098836A1

Abstract

A gearbox (10) having at least two gears (20a,20b) is provided. The gearbox (10) comprises a shift selector, a first gearshaft (14), a second gearshaft (20) selectively engagable with the first gearshaft (14) via the at least two gears (20a,20b), and a first clutch mechanism (62) located on the second gearshaft (20). The first clutch mechanism (62) is adapted to selectively engage the second gearshaft (20) with the first gearshaft (14). The first clutch mechanism (62) comprises a clutch plate (64) attached to first gear (20a) on the second gearshaft (20), and a pressure plate (66) attached to the second gearshaft (20). The clutch plate (64) and pressure plate (66) are adapted to selectively engage one another so that the second gearshaft (20) engages the first gearshaft (14).

Description

Field of the Invention

The present invention is directed to gearboxes for vehicles. More specifically, the present invention is directed to a gearbox having a clutch for synchronising the rotational speeds of two gearshafts in the gearbox.

Background of the Invention

Conventional gearboxes for vehicles employ synchroniser rings to ensure smooth shifts between gears in the gearbox. The synchroniser rings ensure that the shift collar and desired gear make frictional contact before the teeth of the collar engage the gear. In this way, the rotational speeds of the gearshafts in the gearbox are progressively synchronised, thereby allowing a gearshift to take place without any mis-engagement of the collar teeth and desired gear.
A disadvantage of synchroniser rings is that they add significantly to the cost of manufacture of a gearbox. There have therefore been a number of proposals put forward in order to remove the need for synchroniser rings in gearboxes. In removing the synchroniser rings, there is a need to ensure synchronisation of the rotational speeds of the gearshafts in another way before a gearshift can be allowed to take place. Otherwise, the mis-engagement problem referred to above can still occur, leading to problems in achieving a shift and also potentially damaging the gearbox components. Therefore, when removing the synchroniser rings from a gearbox it is important to ensure that a shift cannot take place until the synchronisation of the gearshaft speeds has occurred.
Synchroniser-less shifting mechanisms have been previously proposed. GB-A-2335010 , which shows the features according to the preamble according to claim 1, discloses a synchronising unit which synchronises the rotational speeds of a layshaft and output shaft in a gearbox. The unit comprises first and second auxiliary gears which are fitted to respective first ends of the layshaft and output shaft. The unit further comprises a solenoid-controlled clutch on the output shaft for accelerating the layshaft, and a solenoid-controlled brake for slowing down the layshaft. The brake is applied to one of the first or second auxiliary gears to slow the layshaft. A controller monitors shaft speeds and gear selector positions in order to control the unit.
A disadvantage of the unit disclosed in GB '010 is that the unit is fitted as a "bolt-on" onto the end of the gearbox, so that the auxiliary gears can be fitted onto the ends of the respective shafts. As a result, adding the unit to a gearbox increases the overall size of the gearbox. In the vast majority of vehicles, it is important that gearboxes are of certain dimensions so that they fit within the spaces designed for them. The unit of GB '010 can therefore compromise design requirements in existing vehicles and in many instances would prove difficult to retro-fit to conventional gearboxes due to the increased size.
A further disadvantage of the unit of GB '010 is the added weight and complexity of introducing a brake to slow down the layshaft. In using a brake, a number of further mechanical components are added to the gearbox. Not only do these components increase the overall weight of the gearbox, but they will also be subjected to very large friction forces. By increasing the complexity of the gearbox and subjecting the added components to such forces, the risk of malfunction or breakdown is also increased.
DE-A1-19931770 discloses a gearbox in which a clutch is provided on the output shaft in order to synchronise the rotational speeds of the output shaft and countershaft.
It is an aim of the present invention to obviate or mitigate one or both of the aforementioned disadvantages.
EP- A1- 18 98 128 , an earlier application of the present applicant, which represents also a state of the art published after the filing date of the present application, discloses a gearbox, in which a clutch mechanism is located between a lay shaft and an output shaft to selectively engage the output shaft with the lay shaft in order to match the rotational speeds of the lay shaft and the output shaft.

Summary of the Invention

According to a first aspect of the present invention, there is provided a gearbox having at least two gears and comprising the features according to claim 1. The sub-claims disclose further preferred developments of the invention.
According to a second aspect of the present invention, there is provided a vehicle including a gearbox according to the first aspect of the invention.

Brief description of the drawing

A preferred embodiment of the present invention will now be described, by way of example only with reference to the accompanying drawings, in which:

Figure 1 shows a schematic cut-away view of a gearbox according to a preferred embodiment of the present invention;
Figure 2 shows a detail view of a clutch mechanism shown in Figure 1; and
Figure 3 shows a flowchart of the steps taken by a controller of the gearbox of Figure 1.

Detailed description of the drawing

The gearbox shown in Figure 1, and generally designated 10, comprises a housing 11 and a plurality of co-operating shafts rotatably supported therein. A power input shaft 12 is connected to an external motive power source, typically the crankshaft of an internal combustion engine (not shown). Located on the power input shaft 12 are forward and reverse clutch mechanisms, also known as clutch packs, 16,18. The forward clutch mechanism 16 is adapted to selectively engage the power input shaft 12 and a first gearshaft 14 and cause rotation of the first gearshaft 14 in a first direction. This is effected by way of a first clutch gear 13 whose teeth are permanently engaged with corresponding teeth on a first fixed gear 14a on the first gearshaft 14. When the forward clutch mechanism 16 is disengaged, the power input shaft 12 does not rotate the first gearshaft 14, as there is no connection between the power input shaft 12 and the first clutch gear 13. When the forward clutch mechanism 16 is engaged, the power input shaft 12 is connected to the first clutch gear 13 and hence the first gearshaft 14.
The reverse clutch mechanism 18 is adapted to selectively engage the power input shaft 12 and the first gearshaft 14 and cause rotation of the first gearshaft 14 in a second direction opposite to the first direction. This is effected by way of a second clutch gear 15 whose teeth are permanently engaged with the teeth of a first idler gear 24 fixed at a first end of an idler shaft 22. A second idler gear 26 is fixed to the opposite end of the idler shaft 22 and has teeth which are in permanent engagement with the teeth of the first fixed gear 14a on the first gearshaft 14.
For illustrative purposes, the idler shaft 22 has been shown in Figure 1 lying alongside the power input shaft 12. In reality, as will be appreciated by those skilled in the art, the idler shaft 12 is located in proximity to both the power input shaft 12 and first gearshaft 14 so that the idler gears 24,26 may engage the respective gears of those shafts, as described above.
When the reverse clutch mechanism 18 is disengaged, the power input shaft 12 does not rotate the idler shaft 22 and first gearshaft 14, as there is no connection between the power input shaft 12 and the second clutch gear 15. When the reverse clutch mechanism 18 is engaged, the power input shaft 12 is connected to the second clutch gear 15, the idler shaft 22 and hence the first gearshaft 14. By introducing the idler shaft 22, it will be clear that the direction of rotation of the first gearshaft 14 will be opposite to that when the forward clutch mechanism 16 is engaged.
The illustrated embodiment of the gearbox is suitable for use in a vehicle or work machine which has a number of forward and reverse gears. Whichever clutch is deployed will depend on the direction of travel of the vehicle. It will be appreciated that in normal operating conditions only one clutch mechanism 16,18 can be engaged at a time.
The first gearshaft 14 has a plurality of fixed gears 14a-14d fixed thereto. Each of the fixed gears 14a-14d is permanently engaged with a corresponding gear 20a-20d on a second gearshaft 20. In the conventional manner, each gear 20a-20d is supported on the second gearshaft 20 by a bearing (not shown). Thus, the gears 20a-20d can rotate independently of the second gearshaft 20. Also located on the second gearshaft 20 are a pair of shift collars 27,28 which rotate with the second gearshaft 20 but can move axially back and forth on the gearshaft 20 to engage respective pairs of gears. In the illustrated embodiment, the first collar 27 engages first and second gears 20a,20b, while the second collar 28 engages third and fourth gears 20c.20d.
Rotatably fixed to the second gearshaft 20 is an output gear 60. The output gear 60 is located on the end of the second gearshaft 20 adjacent first gear 20a, and is engaged with a gear on a power output shaft (neither shown).
As shown in detail in Figure 2, first gear 20a is the largest diameter gear on the second gearshaft 20 in permanent engagement with the first gearshaft 14. First gear 20a and the output gear 60 make up an auxiliary clutch mechanism 62. The side of first gear 20a facing the output gear 60 has a clutch plate 64 attached thereto, while the side of the output gear 60 facing first gear 20a has a pressure plate 66 attached thereto. In the same manner as the shift collars 27,28, the output gear 60 rotates with the second gearshaft 20, but can move axially along the shaft 20. An adjustment mechanism comprising a hydraulic piston 68 is attached to the output gear 60. The piston 68 can be selectively actuated by hydraulic fluid entering through a fluid passage 70 in order to move the output gear axially into and out of contact with first gear 20a.
Referring again to Figure 1, each shift collar 27,28 is attached to a respective shift rod via a shift fork 40,42. In the illustrated embodiment, only the second shift rod 44 associated with third and fourth gears 20c,20d is shown, as the first shift rod associated with first and second gears 20a,20b is hidden behind the second shift rod. However, the shift fork 40 associated with the first shift rod can be clearly seen. Each shift rod is preferably selectively connected to a gearstick (not shown) in a conventional manner, wherein the shift rods and gearstick form a shift selector.
Each of the shift rods is provided with a shift hold means adapted to selectively hold the shift rod from entering a desired gear. The shift hold means is preferably a detent comprising a groove 50 in the shift rod and a ball 52 adapted to be selectively received in the groove 50. Preferably, the ball 52 is biased towards the shift rod by a biasing means, most preferably a spring 54. The shift hold means also includes an actuator (not shown) adapted to selectively move the ball 52 out of the groove 50 against the force of the spring 54. The actuator is preferably electromagnetically or hydraulically operated.
A controller (not shown), preferably in the form of an electronic control unit (ECU), is provided to control the gearbox. Speed sensors (not shown) are used to monitor the rotational speeds of the first and second gearshafts 14,20 and relay those speeds to the controller. A shift position sensor (not shown) is also provided which detects the shift being made by an operator and again relays information concerning the shift to the controller. The controller is also in communication with the shift hold means and can actuate the shift hold means in order to release the shift rod so that a gearshift can be made. The forward, reverse and auxiliary clutch mechanisms 16,18,62 are also controlled by signals from the controller.

Industrial applicability

In order to make a shift, the operator will move the gearstick. As the gearstick is moved, the shift sensor detects what the desired gear change is to be, and sends a signal which is received by the controller. Figure 3 shows the processing steps applied by the controller when it detects that a downshift is to be made.
Firstly, at step 100 the controller recognises from the shift sensor that the shift to be made is a downshift. The controller then signals whichever of the forward and reverse clutches 16,18 is currently engaged to disengage at step 102. At the same time, due to the operator shifting out of the present gear, the relevant shift rod will be moved back into a neutral position already held by the remaining shift rods in the gearbox. In moving back into the neutral position, the shift rod allows the biased ball 52 to enter the groove 50 of the detent such that the shift hold means holds the shift rods in that position.
Whilst the shift rods are held in the neutral position by the shift hold means, at step 104 the speed sensors send the controller readings for the rotational speeds of the first and second gearshafts 14,20. At step 106, the controller compares the rotational speeds of the gearshafts 14,20. If both shaft speeds are within a predetermined range where they are substantially synchronised, as at step 108, the controller will actuate the shift hold means in order to release the relevant shift rod. This allows the operator to move the gearstick and shift rod into position in order to shift into the desired new gear at step 110. The controller will then re-apply the forward or reverse clutch 16,18 at step 112 and await the next shift request information from the shift sensor.
If the controller detects that the speeds of the first and second gearshafts 14,20 are outside of the predetermined range and therefore not synchronised, as at step 114, it is necessary to adjust the speed of one or both of the gearshafts 14,20. In such an instance, the controller momentarily engages the auxiliary clutch mechanism 62 at step 116, bringing the output gear 60 and the first gear 20a into contact. This contact utilises the rotation of the second gearshaft 20 caused by the motion of the vehicle to speed up the first gear 20a, which in turns speeds up the first gearshaft 14 through its engagement with first gear 20a.
Once both shaft speeds are within the predetermined range where they are substantially synchronised, as at step 118, the controller will actuate the shift hold means in order to release the relevant shift rod. This allows the operator to move the gearstick and shift rod into position in order to shift into the desired new gear at step 120. The controller will then re-apply the forward or reverse clutch 16,18 at step 122 and await the next shift request information from the shift sensor.
Another manner in which the controller can adjust the speed of the gearshafts 14,20 is by momentarily applying whichever clutch mechanism is not in operation. In other words, if the vehicle is moving forwards and the forward clutch mechanism 16 is engaged, the controller can momentarily engage the reverse clutch mechanism 18. By momentarily engaging the reverse clutch mechanism 18, the reverse clutch 18 applies a frictional force to the power input shaft 12, with the result that both the power input shaft and the first gearshaft 14 slow down. Once the controller detects that the slowing of the first gearshaft 14 has brought the speeds of both gearshafts 14,20 into the predetermined range, it will allow the shift to take place as described above. The same technique can be applied when the reverse clutch mechanism 18 is engaged, but by momentarily engaging the forward clutch mechanism 16.
By locating the auxiliary clutch mechanism on the first gear of the second gearshaft, the present invention can achieve the synchronisation of the shaft speeds on a downshift in the same manner as the prior art, but without having to increase the overall size of the gearbox to do so. Relatively little modification of a conventional gearbox is required to incorporate the arrangement of the present invention, therefore keeping manufacturing costs down. Costs are also controlled in the present invention by the use of existing gearbox components for controlling the speed of the shafts. Aside from the auxiliary clutch, no additional components are needed.
The pressure plate of the auxiliary clutch need not be mounted on an output gear. In fact, the output gear and power output shaft can be dispensed with and the second gearshaft used as the power output shaft. In the case where no output gear is present, the pressure plate can either be mounted directly to the second gearshaft or else mounted on a support which is non-rotatably fixed to the second gearshaft. The adjustment mechanism can then move the plate or support axially on the second gearshaft in the manner previously described. Furthermore, the adjustment mechanism is not limited to a hydraulic piston arrangement. Any other suitable arrangement may also be employed to move the pressure plate.
The first gearshaft of the present invention is preferably a layshaft. However, it should be appreciated that the present invention is not limited to the specific use of a layshaft for the first gearshaft.
Whilst the embodiment of the present invention described above has a number of both forward and reverse gears, the invention is equally applicable to a gearbox having multiple forward gears and only one reverse gear.
Throughout this specification, reference is made to shifting from a first gear to a second gear. For the avoidance of doubt, this does not mean that the invention exclusively relates to shifting between the first and second gears on the second gearshaft. The invention applies to shifts between any of the gears on the second gearshaft.
The shift selector of the illustrated embodiment is comprised of a number of shift rods and a manually-operated gearstick. However, it will be appreciated by those skilled in the art that the shift selector may only comprise one or more shift rods if need be. Furthermore, the shift selector is not limited to the inclusion of a gearstick, although this is preferable. Instead, any other means of manual, semi-automatic or automatic selection of gears may comprise part of the shift selector.
Although the detent is illustrated as comprising a biased ball engaging a groove in the shift rod, the present invention is not limited to use of this specific detent arrangement. Any other suitable detent arrangement may be employed to hold the shift rod.
Finally, whilst the shaft upon which the first and second clutch mechanisms are located has been described in the illustrated embodiment as the power input shaft, it is also possible for that shaft to act as the power output shaft. In other words, the gearbox of the present invention could be used in the opposite arrangement to that described, with the first and second clutch mechanisms located on a power output shaft, and the second gearshaft acting as the power input shaft. In such a case, the output gear and existing power output shaft can be dispensed with.
These and other modifications and improvements may be incorporated without departing from the scope of the invention.

Claims

A gearbox having at least two gears (20a,20b) and comprising:
a shift selector;

a first gearshaft (14);

a second gearshaft (20) upon which the two gears (20a,20b) are rotatably supported, wherein the two gears (20a,20b) are permanently engaged with the first gearshaft (14) and represent the first and second gear ratios of the gearbox; and

a first clutch mechanism (62) located on the second gearshaft (20) and adapted to selectively engage the second gearshaft (20) with the first gearshaft (14), the first clutch mechanism (62) comprising:
a clutch plate (64) rotatably supported on the second gearshaft (20);

a pressure plate (66) non-rotatably attached to the second gearshaft (20);

wherein the clutch plate (64) and pressure plate (66) are adapted to selectively engage one another so that the second gearshaft (20) engages the first gearshaft (14); and

a pressure plate adjustment mechanism adapted to move the pressure plate (66) axially along the second gearshaft (20) in order to selectively engage the clutch plate (64);
characterised in that the clutch plate (64) is attached to the gear (20a) representing the first gear ratio.
The gearbox of Claim 1, further comprising an output gear (60) fixed to the second gearshaft (20), the output gear (60) adapted to drive a power output shaft.
The gearbox of Claim 2, wherein the pressure plate (66) is attached to the output gear (60).
The gearbox of any preceding claim, further comprising:
a shift prevention mechanism adapted to hold the shift selector so as to prevent entry of the shift selector into a second position corresponding with the engagement of the second gear ratio from a first position corresponding with the engagement of the first gear ratio unless the rotational speeds of the first gearshaft (14) and second gearshaft (20) are within a predetermined range; and

a controller adapted to control the shift prevention mechanism.
The gearbox of Claim 4, wherein the shift prevention mechanism comprises:
a position sensor adapted to determine the position of the shift selector;

first and second speed sensors adapted to determine the rotational speeds of the first gearshaft (14) and second gearshaft (20), respectively; and

a shift hold means adapted to selectively hold and release the shift selector;

wherein the controller is adapted to receive information from the sensors and to engage the shift hold means when the rotational speeds of the first gearshaft (14) and second gearshaft (20) are outside the predetermined range such that the shift selector is prevented from entering the second shift position, and release the shift hold means when the rotational speeds of the first gearshaft (14) and second gearshaft (20) are within the predetermined range.
The gearbox of Claim 5, further comprising at least one shift rod (44), and wherein the shift hold means is a detent adapted to selectively engage the shift rod (44) so as to prevent movement thereof.
The gearbox of any of Claims 4 to 6, further comprising a power input shaft (12) and second and third clutch mechanisms (16,18), the second clutch mechanism (16) adapted to effect the selective engagement of the power input shaft (12) with the first gearshaft (14) and cause rotation of the first gearshaft (14) in a first direction; and the third clutch mechanism (18) adapted to effect the selective engagement of the power input shaft (12) with the first gearshaft (14) and cause rotation of the first gearshaft (14) in a second direction opposite to the first direction;
wherein the controller is adapted to adjust the speed of the first gearshaft (14) by either selectively engaging the second clutch mechanism (16) when the first gearshaft (14) is rotating in the second direction, or selectively engaging the third clutch mechanism (18) when the first gearshaft (14) is rotating in the first direction.
The gearbox of any of Claims 4 to 7, wherein the controller is adapted to selectively engage the first clutch mechanism (62) to increase the speed of the first gearshaft (14).
The gearbox of any of Claims 4 to 6, further comprising a power output shaft, and second and third clutch mechanisms (16,18), wherein the second clutch mechanism (16) is adapted to effect the selective engagement of the power output shaft with the first gearshaft (14) and cause rotation of the power output shaft in a first direction; and wherein the third clutch mechanism (18) is adapted to effect the selective engagement of the power output shaft with the first gearshaft (14) and cause rotation of the power output shaft in a second direction opposite to the first direction;
wherein the controller is adapted to adjust the speed of the first gearshaft (14) by either selectively engaging the second clutch mechanism (16) when the power output shaft is rotating in the second direction, or selectively engaging the third clutch mechanism (18) when the power output shaft is rotating in the first direction.
A vehicle including the gearbox of any preceding claim.